This invention relates to a process for the production of aromatic alcohols using improved catalysts.
Aromatic alcohols are useful as intermediates for various types of organic compounds and as solvents, and are advantageously produced industrially by the reduction of aromatic hydroperoxides.
Japanese Patent Publication No.26961/1964 and U.S. Pat. No.2,491,926 disclose methods of producing .alpha.-cumyl alcohol by reducing cumene hydroperoxide or dicumyl peroxide dissolved in cumene with hydrogen in the presence of hydrogenation catalysts such as Pd, Ni, etc. Such reactions are accompanied by the evolution of heat; therefore, use of a solvent is recommended for mitigating reaction heat and for lowering side reactions as much as possible. As said solvents, water-immiscible solvents such as hydrocarbons are employed. However, deactivation of the catalyst is recognized to occur unexpectedly soon when said solvents are used, so, a method of employing a lower aliphatic alcohol is disclosed by Japanese Patent Laid-open No. 69527/1980. Further, in order to obtain aromatic alcohols in good yield a method is disclosed in Japanese Patent Laid open No.174737/1985, wherein said reduction is conducted in coexistence with amines or some compounds capable of being converted to amines during said hydrogenation reaction.
However, in the hydrogenation method described in said Patent Laid-open, a complex process is necessary for the separation of desired aromatic alcohols from aliphatic alcohols, amines, etc. having different properties from those of the aromatic alcohols. In addition, a complex structure of equipment is needed for the separation of the produced alcohols and a suspended catalyst, and therefore, the method mentioned above can not be advantageously employed for industrial mass production thereof.
Japanese Patent Laid-Open No.16843/1984 discloses, when reducing aromatic hydroperoxide with hydrogen gas in the presence of a catalyst containing Pd, a method wherein a feed liquid containing aromatic hydroperoxide is allowed to pass downstream in a fixed bed reactor. Japanese Patent Laid-open No. 110639/1984 discloses, when reducing aromatic hydroperoxide with hydrogen, a method wherein a Pd catalyst with Pd surface area of at least 200m.sup.2 /g Pd is employed in the form of a fixed bed.
It is described that in the hydrogenation method in said patent Laid-open elution of the Pd was barely found, and that the desired aromatic alcohols can be rather effectively obtained. The operating time reported in said patent Laid-open was only 720 hours (30 days), whereas, the present inventors conducted an even longer time of operation to find a completely deactivated catalyst at the 70th day of operation (refer to COMPARATIVE EXAMPLE 2 below). In addition, when we measured the concentrations of Pd in the liquid produced by passing aromatic hydroperoxide solutions having concentrations changed over the Pd catalyst, we recognized a proportional relationship between both concentrations as shown in the next TABLE 1.
TABLE 1 ______________________________________ Concentration of metal in solution Concentration of cumene produced (concentrated 200 times) hydroperoxide in feed (weight by ppm) (weight by %) Pd(0.3%)/.gamma.-alumina catalyst ______________________________________ 2.0 7 4.0 14 8.3 32 16.1 46 ______________________________________
Test liquids were passed at 60.degree. C., and at a LHSV of 6/hour.
That is, as not insignificant quantities of Pd were eluted with aromatic hydroperoxide, the use of a Pd catalyst results in the problem of the inevitable deactivation of the catalyst.
When using a supported Ni catalyst, the catalyst has a disadvantage in spite of having a capacity to reduce aromatic hydroperoxide with hydrogen, of giving a low yield of the desired aromatic alcohols because of many side-reactions (refer to COMPARATIVE EXAMPLE 3 below).
It is an object of the present invention, therefore, to provide a method improved with respect to the catalysts of producing aromatic alcohols wherein no problems such as stated above will occur.